This invention relates generally to radio communication systems and more particularly, it relates to an improved low power RF receiver being responsive to modulated or keyed carrier signals for remotely controlling a number of vehicular devices which has an increased sensitivity over the traditional receivers now available. In particular, the RF receiver of the present invention has specific applications in remotely controlling vehicular devices, such as arming or disarming an alarm system, locking and unlocking doors, opening a trunk or hatch, starting the vehicle, locating or finding a vehicle, and the like. Also, the present RF receiver may be used for garage door operators, for turning ON/OFF of equipment of an entertainment system (radio, television, etc.), and for home security systems.
As is well-known in the prior art, the vehicular security systems or garage door operators typically require the use of superregenerative receivers with keyed carrier transmitters with frequencies operating between 270 MHz and 400 MHz. As specified by the Federal Communications Commission (FCC) under their Rules and Regulations Part 15, Subpart E, the emission of RF energy on the fundamental frequency for a transmitter operating in the frequency range of 260-420 MHz is limited to 3,750 to 12,500 uV/m (linearly interpolated) at 3 m. Further, under this specific FCC classification the spurious emissions from a radio receiver must not exceed 200 uV/m at 3 m in the frequency range between 216-960 MHz. Under this criteria for the transmitter and the superregenerative receiver, the operating distance is usually limited approximately to the range of 100-200 feet.
It would therefore be desirable to provide an RF receiver for receiving signals from a keyed carrier transmitter which has a much improved sensitivity. The present RF receiver performed adequately at distances of over 500 feet away from the transmitter so as to remotely start a vehicle or functioning to locate a vehicle.